As electronic devices such as computers and personal digital assistants (PDAs) have been widely used, users generally record important memos or addresses or the like of friends on the electronic devices instead of pocketbooks.
Particularly, as electronic devices such as tablet personal computers (PCs) and PDAs have been popularized, the users input and record their notes on the electronic devices such as the tablet PCs and the PDAs using pens instead of keyboards. In addition, the users can make simple drawings in addition to notes using application programs such as Paintbrush.
As a method of inputting notes without using a touchscreen or a tablet PC, there is a method of implementing an ultrasonic generating device which generates a reference signal and an ultrasonic signal and is implemented in an input pen for inputting messages, measuring an absolute position of the input pen by using a time difference between the reference signal implemented as an infrared signal or a radio frequency (RF) signal and the ultrasonic signal, and inputting letters or the like by using a trajectory of the input pen moved by a user.
However, a position measurement device as described above in a related art requires ultrasonic sensors that are mounted to the electronic devices such as notebooks and PDAs to receive ultrasonic waves. As a method of mounting the ultrasonic sensors, there are a method of attaching a plurality of ultrasonic sensors to predetermined positions on an outer surface of an electronic device to perform position measurement and removing the attached ultrasonic sensors when the position measurement is terminated, and a method of including the ultrasonic sensors in the electronic device during a manufacturing process of the electronic device.
However, in the former case, there is a problem in that the ultrasonic sensors or frames to which the ultrasonic sensors are mounted have to be prepared. In the latter case, there is a problem in that including a plurality of the ultrasonic sensors for position measurement inputting in the electronic device that may have a small size is difficult.